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ac3dec.c
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1 /*
2  * RAW AC-3 and E-AC-3 demuxer
3  * Copyright (c) 2007 Justin Ruggles <justin.ruggles@gmail.com>
4  *
5  * This file is part of FFmpeg.
6  *
7  * FFmpeg is free software; you can redistribute it and/or
8  * modify it under the terms of the GNU Lesser General Public
9  * License as published by the Free Software Foundation; either
10  * version 2.1 of the License, or (at your option) any later version.
11  *
12  * FFmpeg is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15  * Lesser General Public License for more details.
16  *
17  * You should have received a copy of the GNU Lesser General Public
18  * License along with FFmpeg; if not, write to the Free Software
19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20  */
21 
22 #include "libavutil/crc.h"
23 #include "libavcodec/ac3_parser.h"
24 #include "avformat.h"
25 #include "rawdec.h"
26 
27 static int ac3_eac3_probe(AVProbeData *p, enum AVCodecID expected_codec_id)
28 {
29  int max_frames, first_frames = 0, frames;
30  const uint8_t *buf, *buf2, *end;
31  AC3HeaderInfo hdr;
32  GetBitContext gbc;
34 
35  max_frames = 0;
36  buf = p->buf;
37  end = buf + p->buf_size;
38 
39  for(; buf < end; buf++) {
40  if(buf > p->buf && !(buf[0] == 0x0B && buf[1] == 0x77)
41  && !(buf[0] == 0x77 && buf[1] == 0x0B) )
42  continue;
43  buf2 = buf;
44 
45  for(frames = 0; buf2 < end; frames++) {
46  uint8_t buf3[4096];
47  int i;
48  if(!memcmp(buf2, "\x1\x10\0\0\0\0\0\0", 8))
49  buf2+=16;
50  if (buf[0] == 0x77 && buf[1] == 0x0B) {
51  for(i=0; i<8; i+=2) {
52  buf3[i ] = buf[i+1];
53  buf3[i+1] = buf[i ];
54  }
55  init_get_bits(&gbc, buf3, 54);
56  }else
57  init_get_bits(&gbc, buf2, 54);
58  if(avpriv_ac3_parse_header(&gbc, &hdr) < 0)
59  break;
60  if(buf2 + hdr.frame_size > end)
61  break;
62  if (buf[0] == 0x77 && buf[1] == 0x0B) {
63  av_assert0(hdr.frame_size <= sizeof(buf3));
64  for(i=8; i<hdr.frame_size; i+=2) {
65  buf3[i ] = buf[i+1];
66  buf3[i+1] = buf[i ];
67  }
68  }
69  if(av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0, gbc.buffer + 2, hdr.frame_size - 2))
70  break;
71  if (hdr.bitstream_id > 10)
72  codec_id = AV_CODEC_ID_EAC3;
73  buf2 += hdr.frame_size;
74  }
75  max_frames = FFMAX(max_frames, frames);
76  if(buf == p->buf)
77  first_frames = frames;
78  }
79  if(codec_id != expected_codec_id) return 0;
80  // keep this in sync with mp3 probe, both need to avoid
81  // issues with MPEG-files!
82  if (first_frames>=4) return AVPROBE_SCORE_MAX/2+1;
83  else if(max_frames>200)return AVPROBE_SCORE_MAX/2;
84  else if(max_frames>=4) return AVPROBE_SCORE_MAX/4;
85  else if(max_frames>=1) return 1;
86  else return 0;
87 }
88 
89 #if CONFIG_AC3_DEMUXER
90 static int ac3_probe(AVProbeData *p)
91 {
93 }
94 
95 AVInputFormat ff_ac3_demuxer = {
96  .name = "ac3",
97  .long_name = NULL_IF_CONFIG_SMALL("raw AC-3"),
98  .read_probe = ac3_probe,
99  .read_header = ff_raw_audio_read_header,
100  .read_packet = ff_raw_read_partial_packet,
101  .flags= AVFMT_GENERIC_INDEX,
102  .extensions = "ac3",
103  .raw_codec_id = AV_CODEC_ID_AC3,
104 };
105 #endif
106 
107 #if CONFIG_EAC3_DEMUXER
108 static int eac3_probe(AVProbeData *p)
109 {
110  return ac3_eac3_probe(p, AV_CODEC_ID_EAC3);
111 }
112 
113 AVInputFormat ff_eac3_demuxer = {
114  .name = "eac3",
115  .long_name = NULL_IF_CONFIG_SMALL("raw E-AC-3"),
116  .read_probe = eac3_probe,
117  .read_header = ff_raw_audio_read_header,
118  .read_packet = ff_raw_read_partial_packet,
119  .flags = AVFMT_GENERIC_INDEX,
120  .extensions = "eac3",
121  .raw_codec_id = AV_CODEC_ID_EAC3,
122 };
123 #endif